Pigs are used in pipelines for many reasons including primarily:
1) Scraping the interior of a pipeline to remove rust, encrustation and other solid deposits; PA1 2) To separate one fluid component, whether a liquid or a gas, from a different component; and PA1 3) To provide information about the pipeline.
For whatever reason a pipeline pig is used, it is frequently important to know when the pipeline pig has passed a predetermined location. This information can be used to establish the rate of travel of the pipeline pig and to identify its location in the event the pig becomes stuck or lodged in the pipeline. Further, knowing when a pig moving through a pipeline has passed a specific location can be used for indicating when a sequential pig should be launched into a pipeline and is useful for a variety of other reasons to the operators of pipelines.
Pig signaling devices are well known in the prior art. For reference to pig signaling devices, see the following previously issued U.S. Pat. No. 3,109,410; 4,596,204; 5,279,251; 3,673,628; 4,491,018; 4,857,851 and 4,714,888.
Pig signaling devices can be classified as two basic types, that is, the intrusive type and the non-intrusive type. Intrusive type pig signaling devices include those illustrated in U.S. Pat. Nos. 3,109,410; 4,596,204; 5,279,251 and 4,491,018. The second basic class of pig signaling devices are non-intrusive, that is, where it is not necessary to penetrate the pipeline to detect the passage of a pig. These include devices such as described in U.S. Pat. No. 4,714,888 that indicate passage of a pig by changing magnetic fields, the pig having a magnet that is carried with it. U.S. Pat. No. 4,857,851 is a type of pig signaling device that employs the method of establishing an alternating magnetic field externally of the pipeline and detecting changes in the magnetic field in response to the passage of a pipeline pig.
The present invention is a non-intrusive pipeline pig signaling device that functions in cooperation with a pipeline pig carrying a magnet, that is, the pig signaling device of this invention responds to changing ambient magnetic field intensities adjacent a pipeline when a pig carrying a magnet passes through the pipeline.